FIG. 24 shows a conventional example, i.e., a segmental vulcanizing tire mold, which comprises a fixed lower mold b corresponding to one side wall of a tire, a movable upper mold a movable upward and downward relative to the fixed lower mold b, and a sector c interposed between the molds and corresponding to the tread of the tyre tire f. Needless to say, these members are all annular. The sector c comprises a plurality of segmental blocks arranged circumferentially so as to be easily removable from the tire tread having a pattern of indentations or projections. When an actuator d is raised upon completion of vulcanization, the sector c automatically moves horizontally outward out of contact with the tread of the tire f. When the actuator is further raised, the sector c moves upward therewith. More specifically, each segmental block of the sector c is in engagement with the actuator d at a slide portion extending obliquely downward so as to be horizontally movable outward with the raising of the actuator d. Furthermore, the sector c is pressed on, for example, by the upper mold a so as not to raise until the sector c moves completely out of contact with the tread of the tire f, the sector being upwardly movable only after it has been removed from the tread.
As seen in FIG. 24, when the sector c is adapted to be separated from the upper and lower molds a, b at positions e on the tread surface, the distance the sector c needs to be slidingly moved radially of the tire (so as to be movable upward without contacting the tire tread) can be as short as S1. However, in the case of such separating positions, a stepped portion is likely to occur at the tread surface, or if the separating position coincides with a pattern groove, a crack will develop. If the separating positions are provided on the tire side walls as shown in FIG. 25, an increased sliding distance S2 is required to result in the size of molds becoming larger.
On the other hand, for use with segmental vulcanizing molds for curing retreaded tires, a sector is known which is divided into upper and lower pieces biased by springs or like elastic member and movable into contact with each other by a closing action of a press to close the sector. With this arrangement, the elastic members each have inherent rigidity or become different from each other in rigidity during use, so that the biasing forces of the elastic members are not always the same. Consequently, when the molds are to be closed, the respective divided pieces will not always move from the regular position to upwardly or downwardly shift the parting line of the upper and lower sector pieces, or the sector pieces are likely to move radially (for closing) as displaced from each other, failing to move in synchronism. This entail the drawback that the center (equator) of the tire is positioned off the center of the mold assembly to impair the uniformity of the tire. Further because the sector is opened or closed not horizontally but obliquely, it is impossible to give a great raw cover stretch which is an advantage of the segmental mold (advantage that the raw tire can be made approximate to the finished tire in outside diameter).